The present invention relates to a stator for an electric machine with improved technical vibration and acoustic properties.
Electric machines are used, inter alia, in electrically driven vehicles to drive said vehicles. An electric machine typically comprises a stator on which a plurality of windings which generate a rotational field are arranged. In an internal rotor, a rotor is arranged on a shaft in the stator. The rotor can have permanent magnets or electromagnets. The stator is usually formed by a plurality of pieces of sheet metal arranged one on top of the other, referred to as laminated cores. The invention accordingly also applies to electric machines with an external rotor.
The windings are typically arranged on teeth. Teeth are regions which, in the case of internal rotors, extend inwardly in the radial direction from the essentially cylindrical rotor. When the rotor rotates, an irregularity in the torque is induced by the profile of the inductance which generally fluctuates. This fluctuation in the torque gives rise, inter alia, to acoustic excitations which can be expressed in the form of sound emissions.
In order to reduce the sound emissions, it is known to arrange the teeth obliquely with respect to the axial direction of the stator. Such a stator is described, for example, in DE 10 2010 026 263 A1.
Such a linear oblique arrangement in the electric machine in merely one direction gives rise to an irregular generation of torque in the rotor, in the axial direction of the rotor, said irregular generation giving rise to torsional vibrations, inter alia within the rotor, and as a result to further emissions of sound.
It is proposed to embody the teeth with a double oblique arrangement, for example an arrow-shaped oblique arrangement. However, this results in insulation problems when the oblique angle changes. In particular, the insulation of the groove between the teeth and the use of a sliding cover are critical, since the materials used here are bent and consequently their insulation properties are lost or at least reduced.
The invention is based on the object of providing an electric machine with reduced emissions of sound or excitation of vibrations.
The object of the invention is achieved by a stator, as well as an electric machine having the stator, wherein the stator according to the invention comprises a plurality of teeth which are configured such that a winding can be arranged thereon. The teeth or the grooves between the teeth have a first angle with respect to the longitudinal axis in a first region extending in the axial direction. The teeth or the grooves between the teeth have a second angle with respect to the longitudinal axis in a second region extending in the axial direction of the stator, said second angle being different from the first angle or being opposite to the first angle. The stator has a third region in which the teeth are electrically insulated or are composed of insulation material and which is arranged between the first region and the second region. The third region is arranged in the axial direction between the first and second regions.
In the third region, the teeth have an angle which differs from the first and second angles. Electrical insulation is necessary only in the first and second regions. The insulation of the windings with respect to the stator can therefore be embodied in two stages.
In one embodiment, the insulation can be designed in a single piece. In this case, the insulation in the third region can be implemented by means of selective weakening, for example by use of indents or impressions, in such a way that the insulation material can follow the change in the oblique angle. Consequently, the insulation of the windings of the stator in the region in which the oblique arrangement of the teeth changes from the first angle to the second angle cannot tear. Accordingly, the excitations of vibrations and, therefore, the emission of sound is reduced by the double complementary oblique arrangement. In addition, more uniform torque output is achieved.
The teeth or the groove between them preferably extend in the axial direction in the third region. The teeth and the groove between the teeth can change their angle in the third region so that a transition from the first angle to the second angle is produced.
The first and second regions can be formed at least 50%, more preferably 75%, and most preferably 95%, from a ferromagnetic material. Typically, the first region and the second region each have a laminated core. A laminated core comprises a plurality of sheet metal pieces which are stacked one on the other in the axial direction and are electrically insulated from one another.
In the third region, the teeth can be arranged parallel to the longitudinal axis of the stator. The first region can be formed by a first stator element, the second region can be formed by a second stator element, and the third region can be formed by a third stator element which is arranged between the first stator element and the second stator element and is formed from a material which is electrically nonconductive. In this configuration, the third region is formed by a separate solid stator element.
The third region can include a plurality of elements whose angle can be adjusted with respect to the longitudinal axis. As a result, the stator can be manufactured more easily since abrupt junctions are avoided. The elements can be manufactured from an electrically insulating material.
In another refinement, the first region is formed by a first stator element, the second region is formed by a second stator element and the third region is formed by an insulation layer which is arranged radially inward and partially in the direction of the axial end of the stator on a part of the first region and of the second region. In this refinement, the third region can be formed by a comparatively thin insulation layer, for example a film. In order to avoid air paths and creepage paths the film can be several mm thick.
An electric machine according to the invention comprises the stator described above, windings which are arranged on the teeth of the stator, and at least a first insulation element and at least a second insulation element in the case of a two-part insulation. The at least one first insulation element is arranged on the first region, and the at least one second insulation element is arranged on the second region. The winding is arranged on the first insulation element and the second insulation element.
As has been mentioned above, the insulation elements are embodied in two parts. As a result, bending and/or tearing of an insulation element at the junction between the first angle and the second angle of the toothed stator can be avoided. It is possible to provide an insulation element which covers all the teeth of the first region or of the second region. However, it is also possible to provide a separate insulation element in each groove between two teeth of the stator.
The at least one first insulation element can be arranged on the first region and on a part of the third region, and the at least one second insulation element can be arranged on the second region and on a part of the third region.
A single-piece insulation element can be arranged on the first region, the third region and the second region, and can have at least one flexible region on the third region and/or in the surroundings of the third region.
The invention also relates to a vehicle having the electric machine described above.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.